charging time on new gp3300 pack?

[tamiya4x4dryver]

I just got one of those Radio Shack GP3300 packs yesterday. I cycled it once last night and once tonight. Both times it had been discharged to 5.4 before charging. It reached full charge both times in 35 minutes at a 4.0 amp rate. Seems kinda fast to me??? It seems to be coming off the charge really warm, but not hot, just about right. Does 35 minutes at 4 amps sound right?

[ErikRC10]

that seems a little fast but not to fast. try cycling them a few more times sometimes they take up to 5+ cycles for them to charge/discharge normally.

[kschauwe]

Which charger?

[tamiya4x4dryver]

It's a MRC 959. I've had it a long time and mine is one of the few in existance that actually works right most of the time, LOL.

[guver]

4 amps and 35 minutes is 2333 mah. If it is starting out full charge then the problem is at the bottom. I would bet money on the problem being at the top though, it is not charged all the way up. On the 959 push the display button to read the stop code and if it's not 00 then restart charge, it will finish.

[tamiya4x4dryver]

Yeah, it's weird. I'm taking them down to a 5.4 volt cut-off before charging. Then I'm charging them at 4 amps and setting the threshold to 40 because it was false peaking at 30. When they finish charging, they are certainly warm enough to be done. They aren't timing out and the code has been 00. I have a homemade 4 bulb discharger that I don't really use for cycling, but more to drain the remainder of packs down to 5.4 volts. From a full charge those gp3300's will power those bulbs for 20 minutes and some change, twice what my best gp1600 nicad will do, so it doesn't seem to be lacking in runtime, and the voltage has been really good until they dump. In fact, for a non-matched pack the cells are pretty similar because it dumps very much like a matched pack. So everything seems good to me other than the fact that I can't see how it's only taking 35 minutes at 4 amps. Then again, I had someone tell me that their pack like this takes them 45 minutes at 3 amps, so that's about the same I guess??

[highroller]

Takes roughly 38 to 44 minutes when charging between 6-7amps, with MAH rate being between 3500 to 3800. What may help increase the rates is after discharging down to 5.40 volt level is take pack down more to about 1.50volts but at a lesser load (single 1157 bulb or discharge resistor 1ohm/10watt). My belief is that cells don't pickup or show consistant numbers until it's been used a couple of times - cycling doesn't always help accept if you are trying to get a ballpark idea of cells condition.
Since many NIMH cells are shipped or assembled with a particle charge, discharge the pack first before charging - sometimes especially with matched cells you may get 4000 MAH on the first charge but around 3800 and lower on the cycles thereafter. With the Radio Shack and some regular stick packs number are usually lower because of higher resistance. GP3300 and newer NIMH like to be warm generally bewteen 135 to 145 degrees when peaked. Since cells are not graded it's best to stay with lower rates 4-5amp charge, if you can set the detect - start around 2-3 MV for the first couple of cycles.

[tamiya4x4dryver]

This is probably a long shot, but is it possible that when I have that 959 set on 4 amps, it's really putting out more than 4 amps, like 4.5 or better???

[tamiya4x4dryver]

Highroller, I have a resistor here that was sold by trinity years ago, but it looks like it says 10 watt/ 30 ohm??

[guver]

This is probably a long shot, but is it possible that when I have that 959 set on 4 amps, it's really putting out more than 4 amps, like 4.5 or better???

It is possible because the 959 displays the set-point instead of the actual rate. My experience has been that it is good up to 6 cells then starts falling off and the actual rate is less than the display.

I don't quite understand dischargeing a battery so that one can put more charge back into it , though. If it is full, it is full regardless of what was put into it, right?

2 things come to mind , however. This is to do a c/10 charge for 18 hrs to form the cells or a possible bad/weak cell causeing the low number.

[guver]

Takes roughly 38 to 44 minutes when charging between 6-7amps, with MAH rate being between 3500 to 3800. What may help increase the rates is after discharging down to 5.40 volt level is take pack down more to about 1.50volts but at a lesser load (single 1157 bulb or discharge resistor 1ohm/10watt). My belief is that cells don't pickup or show consistant numbers until it's been used a couple of times - cycling doesn't always help accept if you are trying to get a ballpark idea of cells condition.
Since many NIMH cells are shipped or assembled with a particle charge, discharge the pack first before charging - sometimes especially with matched cells you may get 4000 MAH on the first charge but around 3800 and lower on the cycles thereafter. With the Radio Shack and some regular stick packs number are usually lower because of higher resistance. GP3300 and newer NIMH like to be warm generally bewteen 135 to 145 degrees when peaked. Since cells are not graded it's best to stay with lower rates 4-5amp charge, if you can set the detect - start around 2-3 MV for the first couple of cycles.

6 amps at 44 minutes is 4400 mah
7 amps at 38 minutes is 4433 mah

A charge rate of 1C or more is very nearly 100 %

[tamiya4x4dryver]

I was thinking about fully discharging them and trickle charging them once, but I thought trickle was bad for nimh??? Or is it just bad for performance?

I guess I should clarify another point here.... I'm not racing, I'm just playin around, and to even take that a step further, this pack is going to be used solely in a clod buster with adjustable mounts and 10 tooth pinions and silver can motors. I had another clod set up like this because I could run it around my yard on grass all day long and the motors and batts stayed ambient temp. Plus theres the side benefit of crazy torque to climb with. Anyhow, the moral of this story is that I'm not so much worried about what's good for this battery as far as racing is concerned, just want it to have maximum capacity. From the 2 times I've cycled it, it does seem to power my bulbs twice as long as my 1600's which does make sense, but I just can't believe it's only taking 35 minutes at 4.0 amps. Believe me it's not coming off the charger really hot, but I'd guess that it is 120-140 degrees but no hotter

Thinking about this some more, if you bought these cells outside of r/c, wouldn't these GP3300's be kinda like the nicads and consider a "standard charge" to be 330mah for 14-16 hours?? Wouldn't that make them have killer runtime, but a little mushy as far as punch?? My 959 will charge at a 100 mah trickle and a .5 amp 500 mah charge but they both would time out so that wouldn't be of any use. I do have a 700 mah wall charger for 7.2 volt r/c batteries which I guess I could used for 6 or 7 hours to try that??? Appreciate your help.

[tamiya4x4dryver]

I also meant to say, I noticed this thing is peaking at 8.65 volts?? Good? Bad?

One thing about this 959. It seems just like the old wind up chargers, like as you are charging and the voltage increases, the amp rate drops because of the crappy power supply. Maybe I'm experiencing the opposite, where the voltage is so low, it's actually delivering more than 4 amps?

Not to beat a dead horse, but other than the fact that 35 minutes at 4amps isn't adding up, I can't complain about the performance as far as what they are showing on the bulbs. That's not real scientific or of any use to racers, but face it, if my best gp1600 nicad that's in the prime of it's life will only powewr my 4 bulbs for 11 minutes down to a 5.4 cutoff, and this gp3300 not only powers the bulbs twice that long, but also carries a "heck of a lot" more voltage throughout the entire discharge curve, I'd say I can't be coming up too short here. I'm standing by and waiting for what you guys think I'd be best to do next.

[guver]

Hmm, 8.65 may seem a bit low. Your discharge seems to ad up, but you're right the 4 amps at 35 minutes does not. Do you have a way to measure voltage during the discharge? It should hold at least 7 volts for the 20 minutes.

If you were my neighber or sent it to me I would be happy to produce a discharge graph at 10-15 amps for you, or just do a capacity check on it. How about finding someone with a different digital charger of some sort?

[tamiya4x4dryver]

I don't know anyone around here that does r/c............ I'm not in a position to upgrade my charger right now either. I've had pitbullx3's and millennium pros in the past, but when I got to the point that I just build and mess with alot of tamiya stuff with sport packs and silver can motors, this charger had always worked well for me.

To answer your question, my bulbs have a voltmeter hookup between them and the pack. I was using a stop watch and writing down the voltage in 30 second intervals in order to compare them to my gp1600's. Both cycles produced near exact numbers. Here are the numbers, but keep in mind this is only 4 bulbs and not 10 or 15 so it probably will be showing more voltage than a high amp discharge. It works for my comparison purposes though and like I said, I don't use these to cycle, more to drain off packs when I need to. Here's the numbers:

batt peaked at 8.65, after sitting 30 minutes settled to 8.32, then the roughly 8amp discharge began:

1 min mark 7.48
2 min mark 7.36
3 min mark 7.29
4 min mark 7.27
5 min mark 7.26
6 min mark 7.26
7 min mark 7.25
8 min mark 7.25
9 min mark 7.24
10 min mark 7.22

It finally hit 5.4 volts at the 20:15 mark

[tamiya4x4dryver]

If the standard charge for 3300's is 330ma for 14-16 hours, I could use my 700ma wall charger to charge them for like 7 hours, right? Maybe that would help capacity to do that the one time? Help it fast charge better?

After hitting 5.4, I could also use my 10watt 30 ohm resistor to hit like 1.5 volts like highroller had suggested, correct? I mean before the slow charge.

[tamiya4x4dryver]

While I'm waiting for you guys to reply, I drained them to 5.4 volts on my bulbs, and I've got a resistor and voltmeter hooked to the pack now and am gonna take it down to 1.5 volts, it's slow going...... believe me LOL. When That's done, I'm either gonna charge them on my 700ma wall charger for 7 hours, or I'm gonna do anther 4amp fast charge and time it again. It doesn't seem to me like it's not becoming fully charged, so my best guess is that it wasn't getting fully discharged, although I had taken it down to 5.4 both times.

[highroller]

That resistor has a higher discharge, than a 1ohm/10watt resistor - that was used on their discharge tray.
Times are not exact but rough averages, even then it varies depending on how old each pack was. There should be slight increases in the MAH rates, length of charge and actual voltage at peak by slowly taking cells to a lower voltage. With stick packs you are unable to discharge (equalize) each individual cell -like when it's assemble inline (side by side) so even when using something to discharge the pack to a lower voltage all cells may not end up being at the same voltage levels.
The voltage is good based on load, trickle charging tends to effect the output voltage in use - vehicle may tend to seem flat - not exhibit the good punch (snap) it hard before. Normally when cycling packs, if the first cycle seems inconsistant I wait a day or 2 to give cells time to stablize before repeating it. Waiting 3-6 hours usually gives the impression that cells increased in their voltage but also show a slight decline in runtime, allow a day or two will give a more accurate idea.

[guver]

c/5 rate should be around 120-130 %

700 ma for 7 hrs should do the trick.

[tamiya4x4dryver]

That's what I thought but.......... I discharged ot to 5.4 on the bulbs, then down to 2.6 on the resistor, then used that 700ma wall charger, and at exactly the 5 hour mark, I had to pull the plug because according to my inline voltmeter, it was starting to drop, and the pack was very warm, but not hot. Even though it was technically a trickle charge, it had better voltage and runtime than charging at 4 amps, LOL

after a 30 minute cooldown:

start 8.40v
1 min 7.62v
2 min 7.47v
3 min 7.39v
4 min 7.35v
5 min 7.33v
6 min 7.32v
7 min 7.32v
8 min 7.31v
9 min 7.30v
10min 7.29v
11min 7.27v
12min 7.25v

It hit the 5.40v cutoff at the 21:10 mark. I don't think it's lacking voltage or capacity, do you? Keep in mind that's only a 4 bulb roughly 8 amp discharge so the voltage is probably higher than if it was a 20 or 30 amp discharge I guess.... When I use that bulb discharger I most of the time take the pack down to 2.60 because that Arthur guy from Integy told me once that 5.4 cutoffs are for high drain discharges and 2.6 wouldn't hurt anything if I'm only usin 4 bulbs..... don't know if that's true, but I never have hurt anything. I've actually even kinda noticed that when I'm mostly running Tamiya r/c's with the silver can motors, most of the time, my discharge time on the bulbs is abouyt the same as my runtime with the cars. So those motors most average somewhere around 8-10 amps.

[guver]

It really all seems normal to me, yet I think you should leave it on 700 ma for at least another hour (total of 6-7) to let any cells that are out of balance catch up to all the rest.

I didn't go back thru and read all the posts, but I think that everything you have done has kept the pack as a whole pack and not allowed the cells to balance.